/*
 * (C) 1999 Lars Knoll (knoll@kde.org)
 * Copyright (C) 2004-2016 Apple Inc. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#ifndef WTFString_h
#define WTFString_h

// This file would be called String.h, but that conflicts with <string.h>
// on systems without case-sensitive file systems.

#include "ASCIIFastPath.h"
#include "IntegerToStringConversion.h"
#include "StringImpl.h"

#ifdef __OBJC__
#include <objc/objc.h>
#endif

namespace WTF {

    class ASCIILiteral;

// Declarations of string operations

    WTF_EXPORT_STRING_API int charactersToIntStrict(const LChar *, size_t, bool *ok = nullptr, int base = 10);

    WTF_EXPORT_STRING_API int charactersToIntStrict(const UChar *, size_t, bool *ok = nullptr, int base = 10);

    WTF_EXPORT_STRING_API unsigned charactersToUIntStrict(const LChar *, size_t, bool *ok = nullptr, int base = 10);

    WTF_EXPORT_STRING_API unsigned charactersToUIntStrict(const UChar *, size_t, bool *ok = nullptr, int base = 10);

    int64_t charactersToInt64Strict(const LChar *, size_t, bool *ok = nullptr, int base = 10);

    int64_t charactersToInt64Strict(const UChar *, size_t, bool *ok = nullptr, int base = 10);

    uint64_t charactersToUInt64Strict(const LChar *, size_t, bool *ok = nullptr, int base = 10);

    uint64_t charactersToUInt64Strict(const UChar *, size_t, bool *ok = nullptr, int base = 10);

    intptr_t charactersToIntPtrStrict(const LChar *, size_t, bool *ok = nullptr, int base = 10);

    intptr_t charactersToIntPtrStrict(const UChar *, size_t, bool *ok = nullptr, int base = 10);

    WTF_EXPORT_STRING_API int charactersToInt(const LChar *, size_t, bool *ok = nullptr); // ignores trailing garbage
    WTF_EXPORT_STRING_API int charactersToInt(const UChar *, size_t, bool *ok = nullptr); // ignores trailing garbage
    unsigned charactersToUInt(const LChar *, size_t, bool *ok = nullptr); // ignores trailing garbage
    unsigned charactersToUInt(const UChar *, size_t, bool *ok = nullptr); // ignores trailing garbage
    int64_t charactersToInt64(const LChar *, size_t, bool *ok = nullptr); // ignores trailing garbage
    int64_t charactersToInt64(const UChar *, size_t, bool *ok = nullptr); // ignores trailing garbage
    uint64_t charactersToUInt64(const LChar *, size_t, bool *ok = nullptr); // ignores trailing garbage
    WTF_EXPORT_STRING_API uint64_t charactersToUInt64(const UChar *, size_t, bool *ok = nullptr); // ignores trailing garbage
    intptr_t charactersToIntPtr(const LChar *, size_t, bool *ok = nullptr); // ignores trailing garbage
    intptr_t charactersToIntPtr(const UChar *, size_t, bool *ok = nullptr); // ignores trailing garbage

// FIXME: Like the strict functions above, these give false for "ok" when there is trailing garbage.
// Like the non-strict functions above, these return the value when there is trailing garbage.
// It would be better if these were more consistent with the above functions instead.
    WTF_EXPORT_STRING_API double charactersToDouble(const LChar *, size_t, bool *ok = nullptr);

    WTF_EXPORT_STRING_API double charactersToDouble(const UChar *, size_t, bool *ok = nullptr);

    WTF_EXPORT_STRING_API float charactersToFloat(const LChar *, size_t, bool *ok = nullptr);

    WTF_EXPORT_STRING_API float charactersToFloat(const UChar *, size_t, bool *ok = nullptr);

    WTF_EXPORT_STRING_API float charactersToFloat(const LChar *, size_t, size_t &parsedLength);

    WTF_EXPORT_STRING_API float charactersToFloat(const UChar *, size_t, size_t &parsedLength);

    template<bool isSpecialCharacter(UChar), typename CharacterType>
    bool isAllSpecialCharacters(const CharacterType *, size_t);

    enum TrailingZerosTruncatingPolicy {
        KeepTrailingZeros, TruncateTrailingZeros
    };

    class String {
    public:
        // Construct a null string, distinguishable from an empty string.
        String() {}

        // Construct a string with UTF-16 data.
        WTF_EXPORT_STRING_API String(const UChar *characters, unsigned length);

        // Construct a string by copying the contents of a vector.  To avoid
        // copying, consider using String::adopt instead.
        // This method will never create a null string. Vectors with size() == 0
        // will return the empty string.
        // NOTE: This is different from String(vector.data(), vector.size())
        // which will sometimes return a null string when vector.data() is null
        // which can only occur for vectors without inline capacity.
        // See: https://bugs.webkit.org/show_bug.cgi?id=109792
        template<size_t inlineCapacity, typename OverflowHandler>
        explicit String(const Vector<UChar, inlineCapacity, OverflowHandler> &);

        // Construct a string with UTF-16 data, from a null-terminated source.
        WTF_EXPORT_STRING_API String(const UChar *);

        // Construct a string with latin1 data.
        WTF_EXPORT_STRING_API String(const LChar *characters, unsigned length);

        WTF_EXPORT_STRING_API String(const char *characters, unsigned length);

        // Construct a string with latin1 data, from a null-terminated source.
        WTF_EXPORT_STRING_API String(const LChar *characters);

        WTF_EXPORT_STRING_API String(const char *characters);

        // Construct a string referencing an existing StringImpl.
        String(StringImpl &);

        String(StringImpl *);

        String(Ref<StringImpl> &&);

        String(RefPtr<StringImpl> &&);

        String(Ref<AtomicStringImpl> &&);

        String(RefPtr<AtomicStringImpl> &&);

        // Construct a string from a constant string literal.
        WTF_EXPORT_STRING_API String(ASCIILiteral characters);

        // Construct a string from a constant string literal.
        // This constructor is the "big" version, as it put the length in the function call and generate bigger code.
        enum ConstructFromLiteralTag {
            ConstructFromLiteral
        };

        template<unsigned charactersCount>
        String(const char (&characters)[charactersCount], ConstructFromLiteralTag) : m_impl(
                StringImpl::createFromLiteral<charactersCount>(characters)) {}

        // We have to declare the copy constructor and copy assignment operator as well, otherwise
        // they'll be implicitly deleted by adding the move constructor and move assignment operator.
        String(const String &other)
                : m_impl(other.m_impl) {}

        String(String &&other)
                : m_impl(WTFMove(other.m_impl)) {}

        String &operator=(const String &other) {
            m_impl = other.m_impl;
            return *this;
        }

        String &operator=(String &&other) {
            m_impl = WTFMove(other.m_impl);
            return *this;
        }

        // Inline the destructor.
        ALWAYS_INLINE ~String() {}

        void swap(String &o) { m_impl.swap(o.m_impl); }

        static String adopt(StringBuffer<LChar> &&buffer) { return StringImpl::adopt(WTFMove(buffer)); }

        static String adopt(StringBuffer<UChar> &&buffer) { return StringImpl::adopt(WTFMove(buffer)); }

        template<typename CharacterType, size_t inlineCapacity, typename OverflowHandler>
        static String adopt(Vector<CharacterType, inlineCapacity, OverflowHandler> &&vector) { return StringImpl::adopt(WTFMove(vector)); }

        bool isNull() const { return !m_impl; }

        bool isEmpty() const { return !m_impl || !m_impl->length(); }

        StringImpl *impl() const { return m_impl.get(); }

        RefPtr<StringImpl> releaseImpl() { return WTFMove(m_impl); }

        unsigned length() const {
            if (!m_impl)
                return 0;
            return m_impl->length();
        }

        const LChar *characters8() const {
            if (!m_impl)
                return 0;
            ASSERT(m_impl->is8Bit());
            return m_impl->characters8();
        }

        const UChar *characters16() const {
            if (!m_impl)
                return 0;
            ASSERT(!m_impl->is8Bit());
            return m_impl->characters16();
        }

        // Return characters8() or characters16() depending on CharacterType.
        template<typename CharacterType>
        inline const CharacterType *characters() const;

        bool is8Bit() const { return m_impl->is8Bit(); }

        unsigned sizeInBytes() const {
            if (!m_impl)
                return 0;
            return m_impl->length() * (is8Bit() ? sizeof(LChar) : sizeof(UChar));
        }

        WTF_EXPORT_STRING_API CString ascii() const;

        WTF_EXPORT_STRING_API CString latin1() const;

        WTF_EXPORT_STRING_API CString utf8(ConversionMode) const;

        WTF_EXPORT_STRING_API CString utf8() const;

        UChar at(unsigned index) const {
            if (!m_impl || index >= m_impl->length())
                return 0;
            return (*m_impl)[index];
        }

        UChar operator[](unsigned index) const { return at(index); }

        WTF_EXPORT_STRING_API static String number(int);

        WTF_EXPORT_STRING_API static String number(unsigned int);

        WTF_EXPORT_STRING_API static String number(long);

        WTF_EXPORT_STRING_API static String number(unsigned long);

        WTF_EXPORT_STRING_API static String number(long long);

        WTF_EXPORT_STRING_API static String number(unsigned long long);

        WTF_EXPORT_STRING_API static String number(double, unsigned precision = 6, TrailingZerosTruncatingPolicy = TruncateTrailingZeros);

        // Number to String conversion following the ECMAScript definition.
        WTF_EXPORT_STRING_API static String numberToStringECMAScript(double);

        WTF_EXPORT_STRING_API static String numberToStringFixedWidth(double, unsigned decimalPlaces);

        // Find a single character or string, also with match function & latin1 forms.
        size_t find(UChar c, unsigned start = 0) const { return m_impl ? m_impl->find(c, start) : notFound; }

        size_t find(const String &str) const { return m_impl ? m_impl->find(str.impl()) : notFound; }

        size_t find(const String &str, unsigned start) const { return m_impl ? m_impl->find(str.impl(), start) : notFound; }

        size_t findIgnoringASCIICase(const String &str) const { return m_impl ? m_impl->findIgnoringASCIICase(str.impl()) : notFound; }

        size_t findIgnoringASCIICase(const String &str, unsigned startOffset) const {
            return m_impl ? m_impl->findIgnoringASCIICase(str.impl(), startOffset) : notFound;
        }

        size_t find(CharacterMatchFunctionPtr matchFunction, unsigned start = 0) const {
            return m_impl ? m_impl->find(matchFunction, start) : notFound;
        }

        size_t find(const LChar *str, unsigned start = 0) const { return m_impl ? m_impl->find(str, start) : notFound; }

        // Find the last instance of a single character or string.
        size_t reverseFind(UChar c, unsigned start = UINT_MAX) const { return m_impl ? m_impl->reverseFind(c, start) : notFound; }

        size_t reverseFind(const String &str, unsigned start = UINT_MAX) const { return m_impl ? m_impl->reverseFind(str.impl(), start) : notFound; }

        // Case insensitive string matching.
        size_t findIgnoringCase(const LChar *str, unsigned start = 0) const { return m_impl ? m_impl->findIgnoringCase(str, start) : notFound; }

        size_t findIgnoringCase(const String &str, unsigned start = 0) const {
            return m_impl ? m_impl->findIgnoringCase(str.impl(), start) : notFound;
        }

        size_t reverseFindIgnoringCase(const String &str, unsigned start = UINT_MAX) const {
            return m_impl ? m_impl->reverseFindIgnoringCase(str.impl(), start) : notFound;
        }

        // Wrappers for find & reverseFind adding dynamic sensitivity check.
        size_t find(const LChar *str, unsigned start, bool caseSensitive) const {
            return caseSensitive ? find(str, start) : findIgnoringCase(str, start);
        }

        size_t find(const String &str, unsigned start, bool caseSensitive) const {
            return caseSensitive ? find(str, start) : findIgnoringCase(str, start);
        }

        size_t reverseFind(const String &str, unsigned start, bool caseSensitive) const {
            return caseSensitive ? reverseFind(str, start) : reverseFindIgnoringCase(str, start);
        }

        WTF_EXPORT_STRING_API Vector<UChar> charactersWithNullTermination() const;

        WTF_EXPORT_STRING_API UChar32 characterStartingAt(unsigned) const; // Ditto.

        bool contains(UChar c) const { return find(c) != notFound; }

        bool contains(const LChar *str, bool caseSensitive = true, unsigned startOffset = 0) const {
            return find(str, startOffset, caseSensitive) != notFound;
        }

        bool contains(const String &str) const { return find(str) != notFound; }

        bool contains(const String &str, bool caseSensitive, unsigned startOffset = 0) const {
            return find(str, startOffset, caseSensitive) != notFound;
        }

        bool containsIgnoringASCIICase(const String &str) const { return findIgnoringASCIICase(str) != notFound; }

        bool containsIgnoringASCIICase(const String &str, unsigned startOffset) const { return findIgnoringASCIICase(str, startOffset) != notFound; }

        bool startsWith(const String &s) const { return m_impl ? m_impl->startsWith(s.impl()) : s.isEmpty(); }

        bool startsWithIgnoringASCIICase(const String &s) const { return m_impl ? m_impl->startsWithIgnoringASCIICase(s.impl()) : s.isEmpty(); }

        bool startsWith(const String &s, bool caseSensitive) const { return m_impl ? m_impl->startsWith(s.impl(), caseSensitive) : s.isEmpty(); }

        bool startsWith(UChar character) const { return m_impl ? m_impl->startsWith(character) : false; }

        template<unsigned matchLength>
        bool startsWith(const char (&prefix)[matchLength], bool caseSensitive = true) const {
            return m_impl ? m_impl->startsWith<matchLength>(prefix, caseSensitive) : !matchLength;
        }

        bool hasInfixStartingAt(const String &prefix, unsigned startOffset) const {
            return m_impl && prefix.impl() ? m_impl->hasInfixStartingAt(*prefix.impl(), startOffset) : false;
        }

        bool endsWith(const String &s) const { return m_impl ? m_impl->endsWith(s.impl()) : s.isEmpty(); }

        bool endsWithIgnoringASCIICase(const String &s) const { return m_impl ? m_impl->endsWithIgnoringASCIICase(s.impl()) : s.isEmpty(); }

        bool endsWith(const String &s, bool caseSensitive) const { return m_impl ? m_impl->endsWith(s.impl(), caseSensitive) : s.isEmpty(); }

        bool endsWith(UChar character) const { return m_impl ? m_impl->endsWith(character) : false; }

        bool endsWith(char character) const { return endsWith(static_cast<UChar>(character)); }

        template<unsigned matchLength>
        bool endsWith(const char (&prefix)[matchLength], bool caseSensitive = true) const {
            return m_impl ? m_impl->endsWith<matchLength>(prefix, caseSensitive) : !matchLength;
        }

        bool hasInfixEndingAt(const String &suffix, unsigned endOffset) const {
            return m_impl && suffix.impl() ? m_impl->hasInfixEndingAt(*suffix.impl(), endOffset) : false;
        }

        WTF_EXPORT_STRING_API void append(const String &);

        WTF_EXPORT_STRING_API void append(LChar);

        void append(char c) { append(static_cast<LChar>(c)); };
        WTF_EXPORT_STRING_API void append(UChar);

        WTF_EXPORT_STRING_API void append(const LChar *, unsigned length);

        WTF_EXPORT_STRING_API void append(const UChar *, unsigned length);

        WTF_EXPORT_STRING_API void insert(const String &, unsigned pos);

        String &replace(UChar a, UChar b) {
            if (m_impl) m_impl = m_impl->replace(a, b);
            return *this;
        }

        String &replace(UChar a, const String &b) {
            if (m_impl) m_impl = m_impl->replace(a, b.impl());
            return *this;
        }

        String &replace(const String &a, const String &b) {
            if (m_impl) m_impl = m_impl->replace(a.impl(), b.impl());
            return *this;
        }

        String &replace(unsigned index, unsigned len, const String &b) {
            if (m_impl) m_impl = m_impl->replace(index, len, b.impl());
            return *this;
        }

        template<unsigned charactersCount>
        ALWAYS_INLINE String &replaceWithLiteral(UChar a, const char (&characters)[charactersCount]) {
            if (m_impl)
                m_impl = m_impl->replace(a, characters, charactersCount - 1);

            return *this;
        }

        WTF_EXPORT_STRING_API void truncate(unsigned len);

        WTF_EXPORT_STRING_API void remove(unsigned pos, int len = 1);

        WTF_EXPORT_STRING_API String substring(unsigned pos, unsigned len = UINT_MAX) const;

        WTF_EXPORT_STRING_API String substringSharingImpl(unsigned pos, unsigned len = UINT_MAX) const;

        String left(unsigned len) const { return substring(0, len); }

        String right(unsigned len) const { return substring(length() - len, len); }

        WTF_EXPORT_STRING_API String convertToASCIILowercase() const;

        WTF_EXPORT_STRING_API String convertToASCIIUppercase() const;

        WTF_EXPORT_STRING_API String convertToLowercaseWithoutLocale() const;

        WTF_EXPORT_STRING_API String convertToLowercaseWithoutLocaleStartingAtFailingIndex8Bit(unsigned) const;

        WTF_EXPORT_STRING_API String convertToUppercaseWithoutLocale() const;

        WTF_EXPORT_STRING_API String convertToLowercaseWithLocale(const AtomicString &localeIdentifier) const;

        WTF_EXPORT_STRING_API String convertToUppercaseWithLocale(const AtomicString &localeIdentifier) const;

        WTF_EXPORT_STRING_API String stripWhiteSpace() const;

        WTF_EXPORT_STRING_API String stripWhiteSpace(IsWhiteSpaceFunctionPtr) const;

        WTF_EXPORT_STRING_API String simplifyWhiteSpace() const;

        WTF_EXPORT_STRING_API String simplifyWhiteSpace(IsWhiteSpaceFunctionPtr) const;

        WTF_EXPORT_STRING_API String removeCharacters(CharacterMatchFunctionPtr) const;

        template<bool isSpecialCharacter(UChar)>
        bool isAllSpecialCharacters() const;

        // Returns the string with case folded for case insensitive comparison.
        // Use convertToASCIILowercase instead if ASCII case insensitive comparison is desired.
        WTF_EXPORT_STRING_API String foldCase() const;

        WTF_EXPORT_STRING_API static String format(const char *, ...) WTF_ATTRIBUTE_PRINTF(1, 2);

        // Returns an uninitialized string. The characters needs to be written
        // into the buffer returned in data before the returned string is used.
        // Failure to do this will have unpredictable results.
        static String createUninitialized(unsigned length, UChar *&data) { return StringImpl::createUninitialized(length, data); }

        static String createUninitialized(unsigned length, LChar *&data) { return StringImpl::createUninitialized(length, data); }

        WTF_EXPORT_STRING_API void split(const String &separator, bool allowEmptyEntries, Vector<String> &result) const;

        void split(const String &separator, Vector<String> &result) const {
            split(separator, false, result);
        }

        WTF_EXPORT_STRING_API void split(UChar separator, bool allowEmptyEntries, Vector<String> &result) const;

        void split(UChar separator, Vector<String> &result) const {
            split(separator, false, result);
        }

        WTF_EXPORT_STRING_API int toIntStrict(bool *ok = nullptr, int base = 10) const;

        WTF_EXPORT_STRING_API unsigned toUIntStrict(bool *ok = nullptr, int base = 10) const;

        WTF_EXPORT_STRING_API int64_t toInt64Strict(bool *ok = nullptr, int base = 10) const;

        WTF_EXPORT_STRING_API uint64_t toUInt64Strict(bool *ok = nullptr, int base = 10) const;

        WTF_EXPORT_STRING_API intptr_t toIntPtrStrict(bool *ok = nullptr, int base = 10) const;

        WTF_EXPORT_STRING_API int toInt(bool *ok = nullptr) const;

        WTF_EXPORT_STRING_API unsigned toUInt(bool *ok = nullptr) const;

        WTF_EXPORT_STRING_API int64_t toInt64(bool *ok = nullptr) const;

        WTF_EXPORT_STRING_API uint64_t toUInt64(bool *ok = nullptr) const;

        WTF_EXPORT_STRING_API intptr_t toIntPtr(bool *ok = nullptr) const;

        // FIXME: Like the strict functions above, these give false for "ok" when there is trailing garbage.
        // Like the non-strict functions above, these return the value when there is trailing garbage.
        // It would be better if these were more consistent with the above functions instead.
        WTF_EXPORT_STRING_API double toDouble(bool *ok = nullptr) const;

        WTF_EXPORT_STRING_API float toFloat(bool *ok = nullptr) const;

        bool percentage(int &percentage) const;

#if COMPILER_SUPPORTS(CXX_REFERENCE_QUALIFIED_FUNCTIONS)
        WTF_EXPORT_STRING_API String isolatedCopy() const &;

        WTF_EXPORT_STRING_API String isolatedCopy() &&;

#else
        WTF_EXPORT_STRING_API String isolatedCopy() const;
#endif

        WTF_EXPORT_STRING_API bool isSafeToSendToAnotherThread() const;

        // Prevent Strings from being implicitly convertable to bool as it will be ambiguous on any platform that
        // allows implicit conversion to another pointer type (e.g., Mac allows implicit conversion to NSString *).
        typedef struct ImplicitConversionFromWTFStringToBoolDisallowedA *(String::*UnspecifiedBoolTypeA);
        typedef struct ImplicitConversionFromWTFStringToBoolDisallowedB *(String::*UnspecifiedBoolTypeB);

        operator UnspecifiedBoolTypeA() const;

        operator UnspecifiedBoolTypeB() const;

#if USE(CF)
        WTF_EXPORT_STRING_API String(CFStringRef);
        WTF_EXPORT_STRING_API RetainPtr<CFStringRef> createCFString() const;
#endif

#ifdef __OBJC__
        WTF_EXPORT_STRING_API String(NSString *);

        // This conversion converts the null string to an empty NSString rather than to nil.
        // Given Cocoa idioms, this is a more useful default. Clients that need to preserve the
        // null string can check isNull explicitly.
        operator NSString *() const;
#endif

        WTF_EXPORT_STRING_API static String make8BitFrom16BitSource(const UChar *, size_t);

        template<size_t inlineCapacity>
        static String make8BitFrom16BitSource(const Vector<UChar, inlineCapacity> &buffer) {
            return make8BitFrom16BitSource(buffer.data(), buffer.size());
        }

        WTF_EXPORT_STRING_API static String make16BitFrom8BitSource(const LChar *, size_t);

        // String::fromUTF8 will return a null string if
        // the input data contains invalid UTF-8 sequences.
        WTF_EXPORT_STRING_API static String fromUTF8(const LChar *, size_t);

        WTF_EXPORT_STRING_API static String fromUTF8(const LChar *);

        static String fromUTF8(const char *s, size_t length) { return fromUTF8(reinterpret_cast<const LChar *>(s), length); };

        static String fromUTF8(const char *s) { return fromUTF8(reinterpret_cast<const LChar *>(s)); };
        WTF_EXPORT_STRING_API static String fromUTF8(const CString &);

        // Tries to convert the passed in string to UTF-8, but will fall back to Latin-1 if the string is not valid UTF-8.
        WTF_EXPORT_STRING_API static String fromUTF8WithLatin1Fallback(const LChar *, size_t);

        static String fromUTF8WithLatin1Fallback(const char *s, size_t length) {
            return fromUTF8WithLatin1Fallback(reinterpret_cast<const LChar *>(s), length);
        };

        // Determines the writing direction using the Unicode Bidi Algorithm rules P2 and P3.
        UCharDirection defaultWritingDirection(bool *hasStrongDirectionality = nullptr) const {
            if (m_impl)
                return m_impl->defaultWritingDirection(hasStrongDirectionality);
            if (hasStrongDirectionality)
                *hasStrongDirectionality = false;
            return U_LEFT_TO_RIGHT;
        }

        bool containsOnlyASCII() const;

        bool containsOnlyLatin1() const;

        bool containsOnlyWhitespace() const { return !m_impl || m_impl->containsOnlyWhitespace(); }

        // Hash table deleted values, which are only constructed and never copied or destroyed.
        String(WTF::HashTableDeletedValueType) : m_impl(WTF::HashTableDeletedValue) {}

        bool isHashTableDeletedValue() const { return m_impl.isHashTableDeletedValue(); }

        unsigned existingHash() const { return isNull() ? 0 : impl()->existingHash(); }

#ifndef NDEBUG
        WTF_EXPORT_STRING_API void show() const;
#endif

        // Workaround for a compiler bug. Use operator[] instead.
        UChar characterAt(unsigned index) const {
            if (!m_impl || index >= m_impl->length())
                return 0;
            return (*m_impl)[index];
        }

        // Turns this String empty if the StringImpl is not referenced by anyone else.
        // This is useful for clearing String-based caches.
        void clearImplIfNotShared() {
            if (m_impl && m_impl->hasOneRef())
                m_impl = nullptr;
        }

    private:
        template<typename CharacterType>
        void removeInternal(const CharacterType *, unsigned, int);

        template<typename CharacterType>
        void appendInternal(CharacterType);

        RefPtr<StringImpl> m_impl;
    };

    inline bool operator==(const String &a, const String &b) { return equal(a.impl(), b.impl()); }

    inline bool operator==(const String &a, const LChar *b) { return equal(a.impl(), b); }

    inline bool operator==(const String &a, const char *b) { return equal(a.impl(), reinterpret_cast<const LChar *>(b)); }

    inline bool operator==(const LChar *a, const String &b) { return equal(a, b.impl()); }

    inline bool operator==(const char *a, const String &b) { return equal(reinterpret_cast<const LChar *>(a), b.impl()); }

    template<size_t inlineCapacity>
    inline bool operator==(const Vector<char, inlineCapacity> &a, const String &b) { return equal(b.impl(), a.data(), a.size()); }

    template<size_t inlineCapacity>
    inline bool operator==(const String &a, const Vector<char, inlineCapacity> &b) { return b == a; }


    inline bool operator!=(const String &a, const String &b) { return !equal(a.impl(), b.impl()); }

    inline bool operator!=(const String &a, const LChar *b) { return !equal(a.impl(), b); }

    inline bool operator!=(const String &a, const char *b) { return !equal(a.impl(), reinterpret_cast<const LChar *>(b)); }

    inline bool operator!=(const LChar *a, const String &b) { return !equal(a, b.impl()); }

    inline bool operator!=(const char *a, const String &b) { return !equal(reinterpret_cast<const LChar *>(a), b.impl()); }

    template<size_t inlineCapacity>
    inline bool operator!=(const Vector<char, inlineCapacity> &a, const String &b) { return !(a == b); }

    template<size_t inlineCapacity>
    inline bool operator!=(const String &a, const Vector<char, inlineCapacity> &b) { return b != a; }

    bool equalIgnoringASCIICase(const String &, const String &);

    bool equalIgnoringASCIICase(const String &, const char *);

    template<unsigned length>
    bool equalLettersIgnoringASCIICase(const String &, const char (&lowercaseLetters)[length]);

    template<unsigned length>
    bool startsWithLettersIgnoringASCIICase(const String &, const char (&lowercaseLetters)[length]);

    inline bool equalIgnoringNullity(const String &a, const String &b) { return equalIgnoringNullity(a.impl(), b.impl()); }

    template<size_t inlineCapacity>
    inline bool equalIgnoringNullity(const Vector<UChar, inlineCapacity> &a, const String &b) { return equalIgnoringNullity(a, b.impl()); }

    inline bool operator!(const String &str) { return str.isNull(); }

    inline void swap(String &a, String &b) { a.swap(b); }

#ifdef __OBJC__

    // Used in a small number of places where the long standing behavior has been "nil if empty".
    NSString * nsStringNilIfEmpty(const String&);

#endif

// Definitions of string operations

    inline String::String(StringImpl &impl)
            : m_impl(&impl) {
    }

    inline String::String(StringImpl *impl)
            : m_impl(impl) {
    }

    inline String::String(Ref<StringImpl> &&impl)
            : m_impl(WTFMove(impl)) {
    }

    inline String::String(RefPtr<StringImpl> &&impl)
            : m_impl(WTFMove(impl)) {
    }

    inline String::String(Ref<AtomicStringImpl> &&impl)
            : m_impl(WTFMove(impl)) {
    }

    inline String::String(RefPtr<AtomicStringImpl> &&impl)
            : m_impl(WTFMove(impl)) {
    }

    template<size_t inlineCapacity, typename OverflowHandler>
    String::String(const Vector<UChar, inlineCapacity, OverflowHandler> &vector)
            : m_impl(vector.size() ? StringImpl::create(vector.data(), vector.size()) : Ref<StringImpl>(*StringImpl::empty())) {
    }

    template<>
    inline const LChar *String::characters<LChar>() const {
        ASSERT(is8Bit());
        return characters8();
    }

    template<>
    inline const UChar *String::characters<UChar>() const {
        ASSERT(!is8Bit());
        return characters16();
    }

    inline bool String::containsOnlyLatin1() const {
        if (isEmpty())
            return true;

        if (is8Bit())
            return true;

        const UChar *characters = characters16();
        UChar ored = 0;
        for (size_t i = 0; i < m_impl->length(); ++i)
            ored |= characters[i];
        return !(ored & 0xFF00);
    }

#ifdef __OBJC__

    inline String::operator NSString *() const
    {
        if (!m_impl)
            return @"";
        return *m_impl;
    }

    inline NSString * nsStringNilIfEmpty(const String& string)
    {
        if (string.isEmpty())
            return nil;
        return *string.impl();
    }

#endif

    inline bool String::containsOnlyASCII() const {
        if (isEmpty())
            return true;

        if (is8Bit())
            return charactersAreAllASCII(characters8(), m_impl->length());

        return charactersAreAllASCII(characters16(), m_impl->length());
    }

    WTF_EXPORT_STRING_API int codePointCompare(const String &, const String &);

    inline bool codePointCompareLessThan(const String &a, const String &b) {
        return codePointCompare(a.impl(), b.impl()) < 0;
    }

    template<typename CharacterType>
    inline void appendNumber(Vector<CharacterType> &vector, unsigned char number) {
        int numberLength = number > 99 ? 3 : (number > 9 ? 2 : 1);
        size_t vectorSize = vector.size();
        vector.grow(vectorSize + numberLength);

        switch (numberLength) {
            case 3:
                vector[vectorSize + 2] = number % 10 + '0';
                number /= 10;
                FALLTHROUGH;

            case 2:
                vector[vectorSize + 1] = number % 10 + '0';
                number /= 10;
                FALLTHROUGH;

            case 1:
                vector[vectorSize] = number % 10 + '0';
        }
    }

    template<bool isSpecialCharacter(UChar), typename CharacterType>
    inline bool isAllSpecialCharacters(const CharacterType *characters, size_t length) {
        for (size_t i = 0; i < length; ++i) {
            if (!isSpecialCharacter(characters[i]))
                return false;
        }
        return true;
    }

    template<bool isSpecialCharacter(UChar)>
    inline bool String::isAllSpecialCharacters() const {
        size_t len = length();

        if (!len)
            return true;

        if (is8Bit())
            return WTF::isAllSpecialCharacters<isSpecialCharacter, LChar>(characters8(), len);
        return WTF::isAllSpecialCharacters<isSpecialCharacter, UChar>(characters16(), len);
    }

// StringHash is the default hash for String
    template<typename T>
    struct DefaultHash;
    template<>
    struct DefaultHash<String> {
        typedef StringHash Hash;
    };

    template<>
    struct VectorTraits<String> : SimpleClassVectorTraits {
    };

    class ASCIILiteral {
    public:
        explicit ASCIILiteral(const char *characters) : m_characters(characters) {}

        operator const char *() { return m_characters; }

    private:
        const char *m_characters;
    };

// Shared global empty string.
    WTF_EXPORT_STRING_API const String &emptyString();

    template<unsigned length>
    inline bool equalLettersIgnoringASCIICase(const String &string, const char (&lowercaseLetters)[length]) {
        return equalLettersIgnoringASCIICase(string.impl(), lowercaseLetters);
    }

    inline bool equalIgnoringASCIICase(const String &a, const String &b) {
        return equalIgnoringASCIICase(a.impl(), b.impl());
    }

    inline bool equalIgnoringASCIICase(const String &a, const char *b) {
        return equalIgnoringASCIICase(a.impl(), b);
    }

    template<unsigned length>
    inline bool startsWithLettersIgnoringASCIICase(const String &string, const char (&lowercaseLetters)[length]) {
        return startsWithLettersIgnoringASCIICase(string.impl(), lowercaseLetters);
    }

    template<>
    struct IntegerToStringConversionTrait<String> {
        using ReturnType = String;
        using AdditionalArgumentType = void;

        static String flush(LChar *characters, unsigned length, void *) { return {characters, length}; }
    };

}

using WTF::CString;
using WTF::KeepTrailingZeros;
using WTF::String;
using WTF::emptyString;
using WTF::appendNumber;
using WTF::charactersAreAllASCII;
using WTF::charactersToIntStrict;
using WTF::charactersToUIntStrict;
using WTF::charactersToInt64Strict;
using WTF::charactersToUInt64Strict;
using WTF::charactersToIntPtrStrict;
using WTF::charactersToInt;
using WTF::charactersToUInt;
using WTF::charactersToInt64;
using WTF::charactersToUInt64;
using WTF::charactersToIntPtr;
using WTF::charactersToDouble;
using WTF::charactersToFloat;
using WTF::equal;
using WTF::find;
using WTF::isAllSpecialCharacters;
using WTF::isSpaceOrNewline;
using WTF::reverseFind;
using WTF::ASCIILiteral;

#include <wtf/text/AtomicString.h>

#endif
